Appendix E
Process for creating *.parcel files from TIGER/Line road centerline files and county parcel geometry files
This appendix documents the method we used to generate *.parcel files from road centerline files and county assessors’ office parcel geometry files. A python script implementing this method can be found at https://github.com/vibe-lab-gsd/ozfs-standard/blob/main/data-assembly-code/Intro_PECT.py. A more throrough description of the method can be found at https://tidyparcel-documentation.netlify.app/.
The OZFS *.parcel file identifies each parcel edge as a line string that is labeled as one of five types:
frontindicates that this is a line string representing the front of a parcel.rearindicates that this is line string representing the rear of a parcel.interior sideindicates that this is a line string representing the interior side of a parcel (the side adjacent to another parcel).exterior sideindicates that this is a line string representing the exterior side of a parcel. Only a corner lot can have an exterior side. This is the side of a corner lot that is adjacent (and approximately parallel) to the street that is not indicated in the parcel’s address.unknownindicates that this is a line string representing the side of a parcel that has not been classified into one of the above categories (for irregular parcel geometries and/or parcels where the relationship to the adjacent street network is unclear).
County assessors offices commonly maintain GIS files that store the boundaries of each parcel as a polygon. To convert these to a set of labeled line strings, we first classified each parcel into one of several types, and then applied one of several methods for classifying parcel edges depending on the parcel type.
Classifying parcel types
Accurately classifying parcels is a crucial step to enhance the precision of our final side classification. Given the complexity of urban parcel shapes, we categorized them into several types, each requiring a distinct approach to labeling parcel edges.
Irregular addresses
The front of a parcel is identified based in part on its orientation to the street in the street centerline file that shares a name with the street in the parcel address. Parcels with duplicated addresses, those without addresses, or those with addresses indicating streets that are not included in the street centerline file are classified as separate parcel types.
For parcels with irregular addresses, the front of the parcel is identified as the closest segment to the nearest road centerline that is nearly parallel (a difference in bearing of no more than 20 degrees) to that centerline. The edge that is farthest from the road centerline will be identified as the rear. Any remaining edges that are adjacent to another parcel will be classified as interior_side and those that are not adjacent to another parcel will be classified as exterior_side.
If the above method does not result in a parcel with four edges, including one front and one rear, all parcel edges are re-classified as unknown.
Duplicated Address Parcels
These are typically commercial/public parcels where multiple, separate parcels are recorded under the same address.
No Match Address Parcels
These parcels have address information but the street indicated on the parcel address is not included in the road centerline file.
No Address Parcels
These parcels lack any address data, making them challenging to associate with a road centerline.
Jagged Parcels
Parcels without an irregular address that have at least six edges and a high (greater than 50th percentile for its county) shape index (perimeter to area ratio) are classified as jagged parcels.
We have not attempted to label the sides of jagged parcels. All sides of these parcels are classified as unknown.
Regular parcels
Regular parcels are approximately rectangular, with four distinct sides that meet at approximately right angles, with two sides approximately parallel to the centerline of the street that shares a name with the parcel address. They are further classified as either inside parcels or corner parcels.
For regular parcels, the front of of the parcel is classified as the edge closest to the road centerline for the road named in the parcel address. The parcel farthest from that road is classified as the rear. Any remaining edges that are adjacent to another parcel will be classified as interior_side and those that are not adjacent to another parcel will be classified as exterior_side.
Regular Inside Parcels
A regular parcel without an exterior_side is classified as a regular inside parcel.
Regular Corner Parcels
A regular parcel with an exterior_side is classified as a regular corner parcel.
Cul-de-sac Parcels
These parcels are typically situated at the end of a cul-de-sac so that the front of the parcel is not parallel with the road centerline. The parcel address shares a street name with the road that ends in a cul-de-sac.
Cul-de-sac parcels will generally have a curved parcel edge (which is commonly the front of the parcel). Adjacent parcel edges with a difference in bearing of less than twenty degrees are treated as part of the same parcel edge.
For cul-de-sac parcels, the side farthest from the road named in the parcel address is classified as the rear. Of the remaining edges, those that are adjacent to other parcels are labeled as interior_side. Of the edges that are neither the rear nor an interior_side, the closest to the road named in the parcel address is labeled as the front, and any remaining edges are labeled as exterior_side.
If the above method does not result in a parcel with four edges, including one front and one rear, all parcel edges are re-classified as unknown.
Curve Parcels
These parcels are not cul-de-sac parcels and have at least one curved edge.
Some parcels appear to be cul-de-sac parcels, because they back a cul-de-sac, but their addresses indicate that the front of the parcel is on a through street. They will classified be classified as curve parcels if they have a curved edge.
Adjacent parcel edges with a difference in bearing of less than twenty degrees are treated as part of the same curved parcel edge.
The edge closest to and approximately parallel to a street sharing a name with the street in parcel address will be labeled as the parcel front, and the side furthest from that street will be labeled as the rear. Of the remaining edges, those that are adjactent to another parcel will be labeled as interior_side and those that are not will be labeled as exterior_side.
If the above method does not result in a parcel with four edges, including one front and one rear, all parcel edges are re-classified as unknown.
Special Parcels
Parcels that have an address that can be matched to a street in the road centerline file, but do not conform to any of the above classifications are categorized as special parcels.
- For the parcels with three distinct edges:
- The nearest edge should be labeled as the “front”, and the farthest edge should be labeled as the “rear”.
- For the remaining edges:
- If it is shared with another parcel, label it as ‘Interior side’.
- If it is not a shared edge, label it as ‘Exterior side’.
- If it is shared with another parcel, label it as ‘Interior side’.
- The nearest edge should be labeled as the “front”, and the farthest edge should be labeled as the “rear”.
- For the parcels with four distinct edges:
- Identify the two edges with the smallest angles and label the nearest as
frontand the farthest asrear.
- For the remaining edges:
- If it is shared with another parcel, label it as ‘Interior side’.
- If it is not a shared edge, label it as ‘Exterior side’.
- If it is shared with another parcel, label it as ‘Interior side’.
- Identify the two edges with the smallest angles and label the nearest as
- For the parcels with another number of distinct edges:
- Identify the edges parallel to the nearest road (
angle < 20).- Label the edge with the smallest distance as the “front” and the edge with the greatest distance as the “rear”.
- For the remaining edges:
- If an edge is also parallel to the nearest road and connects to the front, it should also be labeled as “front”.
- If an edge is also parallel to the nearest road and connects to the rear, it should be labeled as “rear”.
- For any remaining edges:
- If it is between two front edges or within the bounding box of front edges, label it as front.
- If it is between two rear edges or within the bounding box of rear edges, label it as rear.
- If it is between two front edges or within the bounding box of front edges, label it as front.
- For any remaining edges:
- If an edge is also parallel to the nearest road and connects to the front, it should also be labeled as “front”.
- Label the edge with the smallest distance as the “front” and the edge with the greatest distance as the “rear”.
- For the remaining edges:
- If it is shared with another parcel, label it as “Interior side”.
- If it is not a shared edge, label it as “Exterior side”.
- If it is shared with another parcel, label it as “Interior side”.
- Identify the edges parallel to the nearest road (
If the above method does not result in a parcel with four edges, including one front and one rear, all parcel edges are re-classified as unknown.